BLACKBOURN

REAR END BLUES

Unique Cars - - CONTENTS -

MICK MCCRUD­DEN’S

ex­pert ad­vice in UniqueCars is a must-read for me. The spe­cial­ist tips you get from an ex­pe­ri­enced front-line au­to­mo­tive en­gi­neer like Mick are great value. His ‘Diff Jockey’ ar­ti­cle in the last is­sue was a good ex­am­ple. Who knew that grease can be a prac­ti­cal sub­sti­tute for bear­ing blue when you’re check­ing the en­gage­ment of pin­ion and crown-wheel teeth? Makes sense once you know.

If I’m hon­est though, I’ve gen­er­ally left fi­ness­ing dif­f­cen­tre set-ups to ex­perts like Mick. I’ve swapped a few, mind – only mod­est skills are needed to pull a diff-cen­tre from the banjo hous­ing be­fore bolt­ing in a fresh unit.

One episode that did get me on in­ti­mate terms with diff set-up sub­tleties was dur­ing my trou­bled re­la­tion­ship with a clas­sic 1929 Austin 7 Me­teor. For­get shims and bear­ing-blue (or grease for that mat­ter), the baby Austin had ex­ter­nally ac­ces­si­ble ad­justers in the axle-hous­ings each side of the banjo-hous­ing that en­abled you to move the crown­wheel assem­bly lat­er­ally, to ei­ther load up or back off its en­gage­ment with the rigidly sup­ported pin­ion. The good book’s mes­sage was sim­ple: If the diff whines un­der load, back it off a whisker. If it whines on the over-run, wind it in a bit. Ac­tu­ally the task of find­ing the sweet spot was far from be­ing that sim­ple – it in­volved nu­mer­ous stops along the road where you wrig­gled un­der the lit­tle Austin, tools in hand, to have an­other suck-it-and-see go. Thank­fully I got there in the end.

With elec­tronic sta­bil­ity and trac­tion-con­trol sys­tems now the norm in main­stream mo­tor­ing, the once sexy lim­ited-slip diffs and lock­ers have been pushed to­ward the mar­gins; these days it’s mainly mo­tor­sport folk and se­ri­ous 4x4 off-road­ers who use them. Sim­i­larly the ba­sic trick of weld­ing diff spi­dergears, not that un­com­mon a while back, has been al­most con­signed to the dust­bin of car-fet­tling his­tory. It was an in­ex­pen­sive DIY-way to con­sis­tently get the power down via both back wheels. It had its short­com­ings though when used on the road – I re­call mates up­set­ting servo oper­a­tors by leav­ing black rub­ber tracks where they pulled U-turns around the pumps, and oc­ca­sion­ally break­ing half-shafts, and hav­ing to fight for steer­ing re­sponse in some sit­u­a­tions against the diff ’s ef­forts to push the car straight ahead.

My most mem­o­rable dif­f­cen­tre swap came dur­ing a quick HR Holden trip from Mel­bourne to a Gold Coast wed­ding. Just be­fore dawn on wed­ding-day Satur­day, not far south of Maclean on the Pa­cific High­way, a pin­ion bear­ing that had been hum­ming hap­pily through the night at around 75mph let go sud­denly. In a big way…

Even­tu­ally an NRMA towtruck un­loaded us be­side an old garage in Maclean. While the me­chanic had gone for the week­end, my spir­its lifted when the bloke on duty said he knew a cane-farmer nearby who was a back­yard Holden wrecker. Not only was the farmer happy to bring me a good diff-cen­tre, he of­fered a choice of ra­tios. With the deal done – us­ing bor­rowed tools, jack and axle stands, and a sheet of gas­ket pa­per I found be­hind the garage work­bench – I got stuck in.

With the wed­ding in mind (and my planned pre-wed­ding snooze aban­doned) there was a touch of Ley­landBrothers pres­sure on my progress: “Will Mal get the sump back on be­fore the tide comes in?”

While I can’t re­mem­ber whether Mal Ley­land did beat the tide, I do re­mem­ber that we didn’t quite get to Surfers Par­adise in time for the wed­ding. All wasn’t lost though; af­ter thor­oughly de­greas­ing my­self, and tak­ing a brief kip, I was in top form for the re­cep­tion. And the cane-farm diff worked like a charm for as long as I had the HR.

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